I've got a large model with offices, corridors, and stairwells. The stairwells are only semi-heated to 50°F with Unit Heaters equipped with Hot Water Coils, connected to a boiler loop that serves the rest of the building.
I cannot get the sizing to happen properly. I've isolated one stairwell zone to make debugging easier and I've tried playing on all the setpoints but to no avail.
Here is the error log:
** Warning ** Calculated design cooling load for zone=1-STAIR-A ZN is zero.
** ~~~ ** Check Sizing:Zone and ZoneControl:Thermostat inputs.
************* Beginning Plant Sizing Calculations
** Warning ** The design coil load is zero for Coil:Heating:Water 1-STAIR-A ZN UNIT HEATER HEATING COIL
** ~~~ ** The autosize value for maximum water flow rate is zero
** ~~~ ** To change this, input a value for UA, change the heating design day, or lower
** ~~~ ** the system heating design supply air temperature
** Severe ** Autosizing of heating coil UA failed for Coil:Heating:Water "1-STAIR-A ZN UNIT HEATER HEATING COIL"
** ~~~ ** Bad starting values for UA
** ~~~ ** Lower UA estimate = 2.288029 W/m2-K (0.1% of Design Coil Load)
** ~~~ ** Upper UA estimate = 2288.029488 W/m2-K (100% of Design Coil Load)
** ~~~ ** Zone "1-STAIR-A ZN" coil sizing conditions (may be different than Sizing inputs):
** ~~~ ** Coil inlet air temperature = 6.617 C
** ~~~ ** Coil inlet air humidity ratio = 4.434E-003 kgWater/kgDryAir
** ~~~ ** Coil inlet air mass flow rate = 6.611502E-002 kg/s
** ~~~ ** Design Coil Capacity = 0.000 W
** ~~~ ** Design Coil Load = 2288.029 W
** ~~~ ** Coil outlet air temperature = 40.555 C
** ~~~ ** Coil outlet air humidity ratio = 8.000E-003 kgWater/kgDryAir
** ~~~ ** Inadequate water side capacity: in Plant Sizing for this hot water loop
** ~~~ ** increase design loop exit temperature and/or decrease design loop delta T
** ~~~ ** Plant Sizing object = HOT WATER LOOP
** ~~~ ** Plant design loop exit temperature = 82.000 C
** ~~~ ** Plant design loop delta T = 11.111 C
** Fatal ** Preceding water coil sizing errors cause program termination
...Summary of Errors that led to program termination:
..... Reference severe error count=1
..... Last severe error=Autosizing of heating coil UA failed for Coil:Heating:Water "1-STAIR-A ZN UNIT HEATER HEATING COIL"
Here is my isolated model (one stairwell zone and an autosized boiler):
Can someone help please?
EDIT: even after I fix what Chandan said, I can get it to run in my small one-zone model but not in my full model. Note that my hot water plant loop is rated at 180°F with a 40°F deltaT, and that's dictated by the VAV boxes that will represent almost all of my heating anyways. So changing the $\Delta T$ isn't an option
ZoneHVAC:UnitHeater,
1-Stair-A Zn Unit Heater, !- Name
Always On Discrete, !- Availability Schedule Name
Node 1235, !- Air Inlet Node Name
Node 1236, !- Air Outlet Node Name
Fan:ConstantVolume, !- Supply Air Fan Object Type
1-Stair-A Zn Unit Heater Fan, !- Supply Air Fan Name
Autosize, !- Maximum Supply Air Flow Rate {m3/s}
Coil:Heating:Water, !- Heating Coil Object Type
1-Stair-A Zn Unit Heater Heating Coil, !- Heating Coil Name
, !- Supply Air Fan Operating Mode Schedule Name
No, !- Supply Air Fan Operation During No Heating
Autosize, !- Maximum Hot Water or Steam Flow Rate {m3/s}
0, !- Minimum Hot Water or Steam Flow Rate {m3/s}
0.001; !- Heating Convergence Tolerance
Fan:ConstantVolume,
1-Stair-A Zn Unit Heater Fan, !- Name
Always On Discrete, !- Availability Schedule Name
0.7, !- Fan Total Efficiency
250, !- Pressure Rise {Pa}
AutoSize, !- Maximum Flow Rate {m3/s}
0.9, !- Motor Efficiency
1, !- Motor In Airstream Fraction
Node 1235, !- Air Inlet Node Name
1-Stair-A Zn Unit Heater Fan Outlet Node; !- Air Outlet Node Name
Coil:Heating:Water,
1-Stair-A Zn Unit Heater Heating Coil, !- Name
Always On Discrete, !- Availability Schedule Name
Autosize, !- U-Factor Times Area Value {W/K}
Autosize, !- Maximum Water Flow Rate {m3/s}
Node 1233, !- Water Inlet Node Name
Node 1234, !- Water Outlet Node Name
1-Stair-A Zn Unit Heater Fan Outlet Node, !- Air Inlet Node Name
Node 1236, !- Air Outlet Node Name
UFactorTimesAreaAndDesignWaterFlowRate, !- Performance Input Method
Autosize, !- Rated Capacity {W}
82.2, !- Rated Inlet Water Temperature {C}
16.6, !- Rated Inlet Air Temperature {C}
71.1, !- Rated Outlet Water Temperature {C}
32.2, !- Rated Outlet Air Temperature {C}
0.5; !- Rated Ratio for Air and Water Convection
Sizing:Zone,
1-Stair-A Zn, !- Zone or ZoneList Name
SupplyAirTemperature, !- Zone Cooling Design Supply Air Temperature Input Method
14, !- Zone Cooling Design Supply Air Temperature {C}
, !- Zone Cooling Design Supply Air Temperature Difference {deltaC}
SupplyAirTemperature, !- Zone Heating Design Supply Air Temperature Input Method
40, !- Zone Heating Design Supply Air Temperature {C}
, !- Zone Heating Design Supply Air Temperature Difference {deltaC}
0.0085, !- Zone Cooling Design Supply Air Humidity Ratio {kgWater/kgDryAir}
0.008, !- Zone Heating Design Supply Air Humidity Ratio {kgWater/kgDryAir}
90.1-2007 - Office - Stair Ventilation, !- Design Specification Outdoor Air Object Name
, !- Zone Heating Sizing Factor
, !- Zone Cooling Sizing Factor
DesignDay, !- Cooling Design Air Flow Method
0, !- Cooling Design Air Flow Rate {m3/s}
0.000762, !- Cooling Minimum Air Flow per Zone Floor Area {m3/s-m2}
0, !- Cooling Minimum Air Flow {m3/s}
0, !- Cooling Minimum Air Flow Fraction
DesignDay, !- Heating Design Air Flow Method
0, !- Heating Design Air Flow Rate {m3/s}
0.002032, !- Heating Maximum Air Flow per Zone Floor Area {m3/s-m2}
0.1415762, !- Heating Maximum Air Flow {m3/s}
0.3, !- Heating Maximum Air Flow Fraction
1-Stair-A Zn Design Spec Zone Air Dist; !- Design Specification Zone Air Distribution Object Name
